Physicochemical properties of Hebi semi-coke from underground coal gasification and its adsorption for phenol

Groundwater pollution caused by underground coal gasification (UCG) as well as its purification is a great concern for scientific and engineering community. In the present study, a UCG model test of Hebi coal was carried out by air/steam two-stage gasification method. The physicochemical properties of UCG residual semi-coke samples were characterized by SEM, nitrogen adsorption at 77 K and FTIR, respectively. Adsorption experiments of phenol onto semi-coke samples were also performed. The results can be summarized as follows: (a) obvious cracks and small voids were observed in semi-coke samples; (b) compared with raw coal, semi-coke presented a larger BET surface area of 21.6 m2/g, larger pore volume of 0.087 cm3/g and wider pore size distribution with micro pores in size of 1.5-2 nm; (c) surface functional groups such as hydroxyl and carbonyl were partially preserved after gasification; (d) and the maximum removal rate of phenol approximately reached 35%. The dispersion forces between π electrons of aromatic nucleus in semi-coke and phenol ring and the formation of electron donor-acceptor complex make it work for phenol adsorption.